How much April 1st?

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Revision as of 11:52, 29 April 2023 by Denny (talk | contribs) (Postscript)
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In my previous post, I was stating that I might miss April 1st entirely this year, and not as a joke, but quite literally. Here I am chronicling how that worked out. We were flying flight NZ7 from San Francisco to Auckland, starting on March 31st and landing on April 2nd, and here we look into far too much detail to see how much time the plane spent in April 1st during that 12 hours 46 minutes flight. There’s a map below to roughly follow the trip.

5:45 UTC / 22:45 31/3 local time / 37.62° N, 122.38° W / PDT / UTC-7

The flight started with taxiing for more than half an hour. We left the gate at 22:14 PDT time (doesn’t bode well), and liftoff was at 22:45 PDT.. So we had only about an hour of March left at local time. We were soon over the Pacific Ocean, as we would stay for basically the whole flight. Our starting point still had 1 hour 15 minutes left of March 31st, whereas our destination at this time was at 18:45 NZDT on April 1st, so still had 5 hours 15 minutes to go until April 2nd. Amusingly this would also be the night New Zealand switches from daylight saving time (NZDT) to standard time (NZST). Not the other way around, because the seasons are opposite in the southern hemisphere.

6:00 UTC / 23:00 31/3 local time / 37° N, 124° W / PDT / UTC-7

We are still well in the PDT / UTC-7 time zone, which, in general, goes to 127.5° W, so the local time is 23:00 PDT. We keep flying southwest.

6:27 UTC / 22:27 31/3 local time? / 34.7° N, 127.5° W / AKDT? / UTC-8?

About half an hour later, we reach the time zone border, moving out of PDT to AKDT, Alaska Daylight Time, but since Alaska is far away it is unclear whether daylight saving applies here. Also, at this point we are 200 miles (320 km) out on the water, and thus well out of the territorial waters of the US, which go for 12 nautical miles (that is, 14 miles or 22 km), so maybe the daylight saving time in Alaska does not apply and we are in international waters? One way or the other, we moved back in local time: it is suddenly either 22:27pm AKDT or even 21:27 UTC-9, depending on whether daylight saving time applies or not. For now, April 1 was pushed further back.

7:00 UTC / 23:00 31/3 local time? / 31.8° N, 131.3 W / AKDT? / UTC-8?

Half an hour later and midnight has reached San Francisco, and April 1st has started there. We were more than 600 miles or 1000 kilometers away from San Francisco, and in local time either at 23:00 AKDT or 22:00 UTC-9. We are still in March, and from here all the way to the Equator and then some, UTC-9 stretched to 142.5° W. We are continuing southwest.

8:00 UTC / 23:00 31/3 local time / 25.2° N, 136.8° W / GAMT / UTC-9

We are halfway between Hawaii and California. If we are indeed in AKDT, it would be midnight - but given that we are so far south, far closer to Hawaii, which does not have daylight saving time, and deep in international waters anyway, it is quite safe to assume that we really are in UTC-9. So local time is 23:00 UTC-9.

9:00 UTC / 0:00 4/1 local time / 17.7° N, 140.9° W / GAMT / UTC-9

There is no denying it, we are still more than a degree away from the safety of UTC-10, the Hawaiian time zone. It is midnight in our local time zone. We are in April 1st. Our plan has failed. But how long would we stay here?

9:32 UTC / 23:32 31/3 local time / 13.8° N, 142.5° W / HST / UTC-10

We have been in April 1st for 32 minutes. Now we cross from UTC-9 to UTC-10. We jump back from April to March, and it is now 23:32 local time. The 45 minutes of delayed take-off would have easily covered for this half hour of April 1st so far. The next goal is to move from UTC-10, but the border of UTC-10 is a bit irregular between Hawaii, Kiribati, and French Polynesia, looking like a hammerhead. In 1994, Kiribati pushed the Line Islands a day forward, in order to be able to claim to be the first ones into the new millennium.

10:00 UTC / 0:00 4/1 local time / 10° N, 144° W / HST / UTC-10

We are pretty deep in HST / UTC-10. It is again midnight local time, and again April 1st starts. How long will we stay there now? For the next two hours, the world will be in three different dates: in UTC-11, for example American Samoa, it is still March 31st. Here in UTC-10 it is April 1st, as it is in most of the world, from New Zealand to California, from Japan to Chile. But in UTC+14, on the Line Islands, 900 miles southwest, it is already April 2nd.

11:00 UTC / 1:00 4/1 local time / 3° N, 148° W / HST / UTC-10

We are somewhere east of the Line Islands. It is now midnight in New Zealand and April 1st has ended there. Even without the delayed start, we would now be solidly in April 1st local time.

11:24 UTC / 1:24 4/1 local time / 0° N, 150° W / HST / UTC-10

We just crossed the equator.

12:00 UTC / 2:00 4/2 local time / 3.7° S, 152.3° W / LINT / UTC+14

The international date line in this region does not go directly north-south, but goes one an angle, so without further calculation it is difficult to exactly say when we crossed the international date line, but it would be very close to this time. So we just went from 2am local time in HST / UTC-10 on April 1st to 2am local time in LINT / UTC+14 on April 2nd! This time, we have been in April 1st for a full two hours.

(Not for the first time, I wish Wikifunctions would already exist. I am pretty sure that taking a geocoordinate and returning the respective timezone will be a function that will be available there. There are a number of APIs out there, but none of which seem to provide a Web interface, and they all seem to require a key.)

12:44 UTC / 2:44 4/1 local time / 8° S, 156° W / HST / UTC-10

We just crossed the international date line again! Back from Line Island Time we move to French Polynesia, back from UTC+14 to UTC-10 again - which means it switches from 2:44 on April 2nd back to 2:44 on April 1st! For the third time, we go to April 1st - but for the first time we don’t enter it from March 31st, but from April 2nd! We just traveled back in time by a full day.

13:00 UTC / 3:00 4/1 local time / 9.6° S, 157.5° W / HST / UTC-10

We are passing between the Cook Islands and French Polynesia. In New Zealand, daylight saving time ends, and it switches from 3:00 local time in NZDT / UTC+13 to 2:00 local time in NZST / UTC+12. While we keep flying through the time zones, New Zealand declares itself to a different time zone.

14:00 UTC / 4:00 4/1 local time / 15.6° S, 164.5° W / HST / UTC-10

We are now “close” to the Cook Islands, which are associated with New Zealand. Unlike New Zealand, the Cook Islands do not observe daylight saving time, so at least one thing we don’t have to worry about. I find it surprising that the Cook Islands are not in UTC+14 but in UTC-10, considering they are in association with New Zealand. On the other side, making that flip would mean they would literally lose a day. Hmm. That could be one way to avoid an April 1st!

14:27 UTC / 3:27 4/1 local time / 18° S, 167° W / SST / UTC-11

We move from UTC-10 to UTC-11, from 4:27 back to 3:27am, from Cook Island Time to Samoa Standard Time. Which, by the way, is not the time zone in the independent state of Samoa, as they switched to UTC+13 in 2011. Also, all the maps on the UTC articles in Wikipedia (e.g. UTC-12) are out of date, because their maps are from 2008, not reflecting the change of Samoa.

15:00 UTC / 4:00 4/1 local time / 21.3° S, 170.3° W / SST / UTC-11

We are south of Niue and east of Tonga, still east of the international date line, in UTC-11. It is 4am local time (again, just as it was an hour ago). We will not make it to UTC-12, because there is no UTC-12 on these latitudes. The interesting thing about UTC-12 is that, even though no one lives in it, it is relevant for academics all around the world as it is the latest time zone, also called Anywhere-on-Earth, and thus relevant for paper submission deadlines.

15:23 UTC / 3:23 4/2 local time / 23.5° S, 172.5° W / NZST / UTC+12

We crossed the international date line again, for the third and final time for this trip! Which means we move from 4:23 am on April 1st local time in Samoa Standard Time to 3:23 am on April 2nd local time in NZST (New Zealand Standard Time). We have now reached our destination time zone.

16:34 UTC / 4:34 4/2 local time / 30° S, 180° W / NSZT / UTC+12

We just crossed from the Western into the Eastern Hemisphere. We are about halfway between New Zealand and Fiji.

17:54 UTC / 5:52 4/2 local time / 37° S, 174.8°W / NZST / UTC+12

We arrived in Auckland. It is 5:54 in the morning, on April 2nd. Back in San Francisco, it is 10:54 in the morning, on April 1st.


Green is March 31st, Red April 1st, Blue April 2nd, local times during the flight.

Basemap CC-BY-SA by TimeZonesBoy, based on PD by CIA World Fact Book


Altogether, there was not one April 1st, but three stretches of April 1st: first, for 32 minutes before returning to March 31st, then for 2 hours again, then we switched to April 2nd for 44 minutes and returned to April 1st for a final 2 hours and 39 minutes. If I understand it correctly, and I might well not, as thinking about this causes a knot in my brain, the first stretch would have been avoidable with a timely start, the second could have been much shorter, but the third one would only be avoidable with a different and longer flight route, in order to stay West of the international time line, going south around Samoa.

In total, we spent 5 hours and 11 minutes in April 1st, in three separate stretches. Unless Alaskan daylight saving counts in the Northern Pacific, in which case it would be an hour more.

So, I might not have skipped April 1st entirely this year, but me and the other folks on the plane might well have had the shortest April 1st of anyone on the planet this year.

I totally geeked out on this essay. If you find errors, I would really appreciate corrections. Either in Mastodon,, or on Twitter, @vrandecic. Email is the last resort, (The map though is just a quick sketch)

One thing I was reminded of is, as Douglas Adams correctly stated, that writing about time travel really messes up your grammar.

The source for the flight data is here:


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